The present invention relates to hydrometallury. More particularly, it relates to the extraction of cobalt metal values from aqueous solutions by solvent extraction techniques employing certain N-alkylalkanohydroxamic acids as extractants. Further, it relates cobalt complexes of such alkanohydroxamic acids and organic solutions thereof.
Solvent extraction hydrometallurgy is employed in industrial operations to recover valuable metals. The key to implementing this technology has been the availability of suitable metal extractants. Metal extractants, hereinafter extractants, are organic soluble compounds that form organic soluble complexes with metals which allow the transfer of the metal values from an aqueous solution to an organic phase containing the extractant in contact with the aqueous solution, i.e., extraction, which can be represented generally as follows: EQU M.sub.aq +E.fwdarw.ME (1) ##STR1##
Unwanted nonmetallic and, depending upon the extractant and conditions employed, metallic impurities are left behind in the aqueous phase (A) which is discarded or further processed for recycle. The metal in the organic phase (B) is then recovered by an aqueous stripping solution phase (C) as follows: EQU ME+SS.fwdarw.MSS+E (2) ##STR2##
The method by which stripping is done depends upon the nature of the extraction and the metal involved. By the stripping process (2) the extractant is regenerated and recycled repeatedly in the extraction process. The metal, now concentrated and purified in the aqueous stripping solution phase (C) can be recovered by conventional methods.
Such solvent extraction processes for recovering metal values are known. See, for example, Kirk-Othmer, Encyclopedia of Chemical Techology, Third Edition, Vol. 6 pp. 850-851, Vol. 9. pp. 713-714. U.S. Pat. No. 3,224,873 issued Dec. 21, 1965 to R. R. Swanson discloses a solvent extraction process employing certain oxime extractants for the recovery of copper. U.S. Pat. No. 3,276,863 issued Oct. 4, 1966 to J. L. Drobnick et al discloses the separation of nickel and cobalt values using certain oxime extractants. U.S. Pat. No. 3,821,351 issued June 28, 1974 to M. F. Lucid discloses certain N-substituted hydroxamic acids useful as extractants for the recovery of copper, molybdenum, uranium, iron and vanadium. More recently, efforts have been directed to the extraction of cobalt. For example, U.S. Pat. No. 4,196,076 issued Apr. 1, 1980 to A. Fujimoto et al discloses a method of extracting and separating cobalt from nickel using monoesters of phosphonic acid. U.S. Pat. No. 4,210,625 issued July 1, 1980 to D. S. Flett discloses a method for the separation of cobalt from nickel using an ester of phosphoric acid by solvent extraction. U.S. Pat. No. 4,348,367 issued Sept. 7, 1982 to W. A. Rickelton et al discloses a method of extracting cobalt (II) from its aqueous solution using an organic soluble phosphinic acid.
Cobalt is a highly valued metal and aqueous solutions containing cobalt metal values are obtained from processes employed in the hydrometallurgy of ores, the recovery of cobalt and other metals from spent catalysts and the reclaiming of cobalt and other metals from metal scrap. Cobalt occurs in ores that bear nickel, magnesium, copper, lead and zinc.
It is known that cobalt metal values in solution commonly exists as either Co(II) or Co(III) and that these two oxidation states have widely different chemistries when complexed by a ligand. Ligands can be characterized as monodentate which are capable of forming only one bond with the central metal ion and as bidentate which coordinates through two bonds from different parts of the molecule or anion. Co(II) can be converted to Co(III) in the presence of air (oxygen source) depending on the type of ligand used as a metal extractant. Further, it is known that under oxidizing conditions, presence of air, normally Co(II) converts to Co(III) when complexed with a bidentate ligand or chelating agent, i.e., one that bonds to metal ion through at least two atoms thereby, forming a chelate ring complex and that the Co(III) chelate formed is usually irreversible i.e., not readily strippable.
In view of the formation of the Co(III) complexes under aerobic conditions with chelating agents, such agents have not been employed in the solvent extraction of metals from aqueous solutions containing cobalt. Examples of chelating agents known to form irreversible cobalt (III) complexes in the presence of air include the chelating metal extractants used in hydrometallurgy such as the phenolic oximes, available under the tradenames LIX, General Mills, Inc. ACORGA P5000 series, ICI Corporation and SME-529, Shell Chemical, and other known chelating agents, such as ethylenediamine, acetylacetone, oxalic acid, 8-hydroxyquinoline, ethylenediaminetetracetic acid, nitrilotriacetic acid and the like. Accordingly, since monodentate extractants do not form irreversible Co (III) complexes such extractants, for example, derivatives of phosphoric, phosphonic and phosphinic acids, have been developed for the recovery of cobalt in solvent hydrometallurgy.
In view of the much greater activity of chelating agents, such agents are more desirable than monodentate extracts in solvent extraction hydrometallurgy. It has now been discovered that certain N-alkylalkanohydroxamic acid chelating agents reversibly extract cobalt in the presence of air or other oxidizing conditions. This unexpected activity of this class of chelating agents provides an efficient process for extracting cobalt from aqueous solutions containing cobalt by solvent extraction.
Further, this invention provides an effective means to recover cobalt and other valuable metals such as nickel from aqueous feed solutions containing cobalt and nickel metal values.
These and other advantages of the present invention will become apparent from the following description.